1. Field of the Invention
The present invention relates to submersible pump apparatus whose liquid material output can be varied.
2. Description of the Prior Art
In the submersible pump disclosed in my U.S. Pat. No. 4,134,711, issued Jan. 16, 1979, which is designed for location in a sump or the like, a relatively inexpensive and simple way is shown to vary the amount of liquid material pumped to accomodate differential rates of flow of the liquid material into the sump. However, there is lacking a completely satisfactory way to vent air from the back shroud area of the pump impeller to facilitate self-priming and to reduce thrust bearing loads. Further, the venting hardware which is shown for combining the venting function with the spray system for cooling the pump motor is relatively exposed, and it is therefore susceptible to accidental damage.
Prior art devices other than that disclosed in my patent typically either intermittently operate the pump motor according to the sensed level of the liquid material, or control the rate of liquid material discharged by varying the speed of rotation of the pump impeller. Thus, the impeller rotates at higher speeds when the sump is relatively full, and rotates at lower speeds when the liquid level decreases. The impeller speed has been controlled in a number of ways in the prior art. Some devices employ an oil bath or magnetic clutch to vary the impeller speed, while maintaining the speed of the drive motor constant. Other devices vary the speed of the drive motor itself, as by frequency control or the like. All of such systems tend to be relatively expensive and complex.
The present apparatus is similar to the apparatus of my patent, controlling the quantity of liquid material by aspiration or injection of air, but it includes an improved vent and spray apparatus.